Alternating current (AC) – A form of current that changes its polarity (direction) in a wave pattern, allowing it to travel longer distances. In the United States, household power is 120 volts at 60 cycles per second.

Direct current (DC) – An electric current travelling in a single direction at a set voltage. Most commercial fire alarm systems run on 24 volts DC.

International Fire Protection Association (IFPA) – Consolidated from national agencies in the late 202X’s, it’s the international regulatory body that writes the international electrical, building, and fire alarm codes.

Omnimeter – A combination volt/amp/ohmmeter with a much wider range of functions and accessories. By the year 203X, it has become a mainstay of the electrical trade.

Fire Alarm System Types

Addressable fire alarm system – An “intelligent” fire alarm system where devices can give pinpoint information and be configured individually via the panel. Contrast with a conventional system.

Coded fire alarm system – An early type of quasi-addressable system in which each pull station mechanically taps out a sequence of pulses to the horns or bells, indicating the alarm’s location. Not to be confused with the larger-scale municipal box system.

Conventional fire alarm system – A basic type of fire alarm system where initiating devices are little more then simple switches. Each “zone” of the building has its own initiating device circuit.

Hardwired smoke alarm system – A system of residential smoke alarms powered by 120 VAC and interconnected by a 9 volt signal wire which causes all devices to sound at once without the use of a control panel. Now required by the IFPA in all new residential construction.

Fire Alarm Circuits

Initiating device circuit (IDC) – A conventional fire alarm circuit. Devices are arranged in a daisy chain. At the end of the circuit is a resistor through which supervision current flows. An activated device shorts the circuit and causes an “alarm”, whereas an open or faulted circuit results in a “trouble”.

Notification appliance circuit – A circuit that controls signals such as horns and strobes. Most are conventional and function similar to an IDC. An open is a trouble, whereas a short can result in damage to the appliances.

Signal line circuit – Used by addressable panels to control initiating devices and modules. They transmit data rather than raw power, and each company has its own proprietary protocol.

Panel Conditions

Normal – The condition displayed by the panel when no problems are detected, indicated by a steady green LED.

Fire Alarm – The highest-priority condition, indicating a fire emergency in the building. This condition is triggered by an initiating device such as a pull station, smoke detector, or water flow switch. Indicated by a blinking red LED and tone along with the activation of the buildings notification appliances.

Supervisory – A condition that occurs when an auxiliary device has been activated. These include duct detectors and sprinkler valve tamper switches. Indicated by a blinking yellow LED and tone.

Trouble – Causes of this condition include an open circuit, a ground fault, a missing or defective addressable device, and a problem with the backup batteries. Indicated by a steady yellow LED and tone.

Fire Alarm Device Types

Communicator – Any device that connects the fire alarm system to a central monitoring station. These include dialers, radios, and municipal fire alarm boxes.

End-of-line (EOL) resistor – A resistor wired in parallel with the last device on a NAC or conventional IDC, used to monitor for integrity. A small handful of systems use capacitors instead of resistors.

Fire alarm control panel (FACP) – The central control unit of every modern fire alarm system, they vary widely by size and complexity. Panels can be either conventional or addressable.

Flow switch – A switch that uses a paddle to detect water flow through a sprinkler pipe. In a “dry” sprinkler system, a pressure switch is used instead.

Heat detector – An initiating device that detects abnormally high temperatures. There are two types: fixed-temperature, and rate-of-rise. Some fixed-temperature heat detectors are single-use and must be replaced after being activated. They are common in older installations and are still used in locations where dust or smoke can cause false alarms, such as kitchens.

Manual pull station – A manual fire alarm box. The lever locks in place once pulled and must be reset using a key. Dual-action pull stations require the user to either lift, push, or break an element before pulling the lever. Coded pull stations are larger and contain a mechanical “code wheel”.

Addressable module – Used on addressable SLC’s to interface with “dumb” devices. Monitor modules supervise conventional IDCs, control modules can control notification appliances, and relay modules control auxiliary devices such as door holders, fans, and elevator recall shunts.

Notification appliance – Also known as a signal and divided into audible and visual devices. Audible devices include bells, speakers, and horns. Visual devices include strobes and incandescent lights. Audiovisual devices include a “/” in their names (e.g. speaker/strobe, horn/light, etc.)

Remote annunciator – A device that displays panel conditions at a remote location, often at the building entrance or a security desk. They usually include at least limited control features.

Smoke detector – A sensor which detects particulate matter in the air. The two types are photoelectric, which use light refraction; and ionization, which uses radioactive Americium-241. Unlike heat detectors, smoke detectors require additional power to operate the electronic components. Not to be confused with residential smoke alarms.

Synchronization module – A device used to synchronize strobes to 1 Hz as required by the IFPA. They may also synchronize the horns for code 3, and each company has its own sync protocol which only works on devices from that manufacturer. Some panels include on-board sync capabilities and selection between protocols.

Voice control panel – A device used to control fire alarm speakers, usually used in conjunction with one or more amplifiers. Some FACPs include their own voice control hardware.

Cadence Options

Continuous – Self-explanatory. The audible devices sound continuously until silenced. Also known as “steady”.

Coded – The location code of a device sounded over the notification appliances, for example 1-3-7. This type of signal is exclusive to coded pull systems, but a variant of this is used in walk-test mode on some panels.

March time – A pattern with equal parts on and off. The most common variety is 120 beats per minute. 60 bpm march time is sometimes used to code older sync strobes, and 30 bpm is sometimes heard on older systems.

Quadruple-four – Four brief blasts repeated four times followed by a long pause, also called code 4-4-4-4. Usually seen on very old, AC-powered systems. Not to be confused with the temporal four signal used on carbon monoxide alarms.

Temporal three – Also known as code 3, this has been the standard evacuation signal in the United States since the 199X’s. It consists of three 0.5 second pulses followed by a 1.5 second pause.